Steam turbine comprising a thrust balance piston

ABSTRACT

A cooling mechanism for a steam turbine is provided, which has, in the area of the valve connection a cooling channel, into which cooling steam flows from the flow channel, the steam then being fed as cooling steam in the area of the thrust balance piston.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2012/065065 filed Aug. 1, 2012, and claims the benefitthereof. The International Application claims the benefit of EuropeanApplication No. EP 11176574.9 filed Aug. 4, 2011. All of theapplications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a steam turbine having an outer housing and aninner housing, a rotor, comprising a plurality of rotor blades, whichhas a thrust compensating piston being arranged in a rotationallymounted manner within the inner housing, the inner housing having aninner housing end region which is formed around the thrust compensatingpiston, a seal which seals a third pressure space which is arrangedbetween the inner housing region and the outer housing, the innerhousing having a feed channel which connects the first pressure space toa thrust compensating piston pre-space which is arranged between thethrust compensating piston and the inner housing.

BACKGROUND OF INVENTION

In the context of the present application, a steam turbine is understoodto be every turbine or part turbine, through which a working medium inthe form of steam flows. In contrast to this, gas and/or air flowsthrough gas turbines as working medium which, however, is subject tocompletely different temperature and pressure conditions than the steamin a steam turbine. In contrast to gas turbines, for example, theworking medium which flows to a part turbine and is at the highesttemperature at the same time has the highest pressure in steam turbines.An open cooling system which is open to the flow channel can also berealized without external supply of cooling medium in gas turbines. Anexternal supply of cooling medium should be provided for a steamturbine. The prior art concerning gas turbines therefore cannot be usedfor this reason to assess the subject matter of the present application.

A steam turbine usually comprises a rotatably mounted rotor which isfitted with blades and is arranged inside a housing or housing shell. Ifheated and pressurized steam flows through the interior of the flowchannel, which interior is formed by the housing shell, the rotor is setin rotation by the steam via the blades. The blades of the rotor arealso called rotor blades. Moreover, stationary guide blades are usuallyfixed on the inner housing, which guide blades reach into theintermediate spaces of the rotor blades along an axial extent of thebody. A guide blade is usually held at a first point along an inner sideof the steam turbine housing. Here, it is usually part of a guide bladerow which comprises a number of guide blades which are arranged on theinner side of the steam turbine housing along an inner circumference.Here, each guide blade points radially to the inside with its turbineblade. A guide blade row at said first point along the axial extent isalso called a guide blade cascade or guide blade ring. A number of guideblade rows are usually connected one behind another. Accordingly, afurther second blade is held along the inner side of the steam turbinehousing at a second point along the axial extent behind the first point.A pair of a guide blade row and a rotor blade row is also called a bladestage.

The housing shell of a steam turbine of this type can be formed from anumber of housing segments. The housing shell of the steam turbine isunderstood as being, in particular, the stationary housing component ofa steam turbine or of a part turbine, which housing component has aninterior along the longitudinal direction of the steam turbine in theform of a flow channel which is provided for the working medium in theform of steam to flow through. Depending on the type of steam turbine,this can be an inner housing and/or a guide blade carrier which does nothave an inner housing or a guide blade carrier.

For reasons of efficiency, the design of a steam turbine of this typefor what are known as “high steam parameters”, that is to say, inparticular, high steam pressures and/or a high steam temperature, can bedesirable. However, a temperature increase, in particular, is notpossible to an unlimited extent for material reasons. In order to makereliable operation of the steam turbine possible here, even in the caseof particularly high temperatures, cooling of individual structuralelements or components can therefore be desirable. The temperatureresistance of the components is usually limited depending on the choiceof material. Without efficient cooling, substantially more expensivematerials (for example, nickel-based alloys) would be necessary in thecase of rising temperatures.

In the case of the previously known cooling methods, in particular for asteam turbine body in the form of a steam turbine housing or a rotor, adistinction is to be made between active cooling and passive cooling. Inthe case of active cooling, cooling is brought about by a cooling mediumwhich is fed to the steam turbine body separately, that is to say inaddition to the working medium. In contrast, passive cooling takes placemerely by suitable routing or use of the working medium. Up to now,steam turbine bodies have preferably been cooled passively.

In order to achieve higher degrees of efficiency in the case ofelectricity generation by way of fossil fuels, there is the need to usehigher steam parameters in a turbine than previously customary, that isto say higher pressures and temperatures. In high temperature steamturbines, temperatures partly far above 500° C. are provided in the caseof steam as working medium.

The previously known cooling methods for a steam turbine housingprovide, insofar as they are active cooling methods at all, at any ratetargeted incident flow of a separate turbine part to be cooled, and arerestricted to the inflow region of the working medium, at any rate withincorporation of the first guide blade ring. In the case of loading ofcustomary steam turbines with higher steam parameters, this can lead toincreased thermal loading which acts on the entire turbine and could bereduced only insufficiently by an above-described customary coolingarrangement of the housing. Steam turbines which operate in principlewith higher steam parameters in order to achieve higher degrees ofefficiency require improved cooling, in particular of the housing and/orof the rotor, in order to compensate to a sufficient extent for higherthermal loading of the steam turbine. There is the problem here that, ifpreviously customary turbine materials are used, the increasing loadingof the steam turbine body by increased steam parameters can lead todisadvantageous thermal loading of the steam turbine which reduces theservice life. As a consequence of this, it is scarcely possible any moreto produce steam turbines of this type economically.

To this end, it is important, in addition to the rotor and the housingincluding screws, to also design the valve connection itself towithstand high temperatures and high pressures.

SUMMARY OF INVENTION

It is an object of the invention to specify a steam turbine which can becooled particularly effectively even in the high temperature range.

This object is achieved by a steam turbine having the features asdescribed herein.

Advantageous developments are specified further herein.

In one advantageous development, the seal is configured as a pistonring, which leads to rapid and inexpensive manufacture of the steamturbine according to the invention.

In a further advantageous development, the steam turbine comprises avalve for feeding steam into the flow channel, cooling channels beingformed in the valve connection which are connected in terms of flow tothe first pressure space. The cooling channels are advantageouslyconnected in terms of flow to the third pressure space.

The invention proceeds from the concept that inherent cooling ofcomponents is possible, in which a targeted pressure flow is madepossible or is forced via different pressure levels. The pressure in thefirst pressure space is thus greater than the pressure in the thirdpressure space. The cooling channels which are arranged in such a waythat they flow around temperature-loaded components are accordinglyflowed around forcibly by cooler steam. The consequence is that aconsiderable increase in the cooling effect for components of the valveconnection is possible. Said cooling effect is achieved by virtue of thefact that the third pressure space is connected directly to the thrustcompensating piston pre-space.

The cooling channels are advantageously arranged between a valvediffuser and the outer housing.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in greater detail using an exemplaryembodiment. Components with identical designations have substantiallythe same method of operation. In the drawing:

FIG. 1 shows a cross-sectional view of a steam turbine according to theinvention, and

FIG. 2 shows a cross-sectional view, in a section through the inflow ofthe steam turbine according to the invention.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows a cross section through a steam turbine 1. The steamturbine 1 has an outer housing 2 and an inner housing 3. The innerhousing 3 and the outer housing 2 have a fresh steam feed channel whichis described in greater detail in FIG. 2. A rotor 5 which has a thrustcompensating piston 4 is arranged in a rotationally mounted mannerwithin the inner housing 3. The rotor is usually configured so as to berotationally symmetrical about a rotational axis 6. The rotor 5comprises a plurality of rotor blades 7. The inner housing 3 has aplurality of guide blades 8. A flow channel 9 is formed between theinner housing 3 and the rotor 5. The flow channel 9 comprises aplurality of blade stages which are formed in each case from a row ofrotor blades 7 and a row of guide blades 8.

Fresh steam flows via the fresh steam feed channel into an inflowopening 10 and flows from there in a flow direction 11 through the flowchannel 9 which extends substantially parallel to the rotational axis 6.The fresh steam expands and cools in the process. Thermal energy isconverted in the process into rotational energy. The rotor 5 is set in arotational movement and can drive, for example, a generator for electricpower generation.

Depending on the blade type of the guide blades 8 and rotor blades 7,thrust with a greater or lesser magnitude of the rotor 5 is produced inthe flow direction 11. The thrust compensating piston 4 is usuallyconfigured in such a way that a thrust compensating piston pre-space 12is formed and is loaded with a defined pressure. Here, the thrustcompensating piston pre-space 12 is upstream of the thrust compensatingpiston 4 as viewed in the flow direction 11. A counterforce whichcounteracts a thrust force 13 of the blade path is produced by steamhaving a particular pressure being fed into the thrust compensatingpiston pre-space 12.

During operation, steam flows into the inflow opening 10. The freshsteam feed is shown symbolically by the arrow 13 a. Here, the freshsteam usually has temperature values of, for example, up to 625° C. anda pressure of up to 350 bar. The fresh steam flows through the flowchannel 9 in the flow direction 11. After a blade stage, the steam flowsinto the thrust compensating piston pre-space 12 via a connection whichcomprises an outward channel 14, a first pressure space 15 and a feedchannel 16.

In particular, the steam flows into the first pressure space 15 which isformed between the inner housing 3 and the outer housing 2 via anoutward channel 14 which is formed as a communicating tube between afirst pressure space 15 and the flow channel 9 after a blade stage. Apressure of p₁ prevails in said first pressure space 15. The steam whichis situated in the first pressure space 15 between the inner housing 3and the outer housing 2 then has lower temperature and pressure values.Said steam flows via a feed channel 16 which is formed as acommunicating tube between the first pressure space 15 and the thrustcompensating piston pre-space 12.

The thrust compensating piston pre-space 12 is arranged in an axialdirection 17 between the thrust compensating piston 4 and the innerhousing 3. The thrust compensating piston pre-space 12 can also becalled a second pressure space. A pressure p₂ prevails in said secondpressure space.

Fresh steam which flows into the inflow opening 10 flows for thegreatest part through the flow channel 9 in the flow direction 11. Asmaller part flows as leakage steam into a leak sealing space 18. Thisleak sealing space 18 is formed between the inner housing 3 and therotor 5. Here, the leakage steam flows substantially in acounterdirection 19. Here, the counterdirection 19 is oriented in theopposite direction to the flow direction 11. The leakage steam flowsinto the flow channel 9 via a crosswise return channel 20 which as acommunicating tube between the sealing space 18, which is formed betweenthe rotor 5 and the housing 3, and an inflow space 26 which is arrangedafter a blade stage. Here, with respect to the flow direction 11, thecrosswise return channel 20 is formed substantially perpendicularly fromthe sealing space 18 toward the first pressure space 15, substantiallyparallel after a deflection 21 and substantially perpendicularly after asecond deflection 22, without, however, connecting the sealing space 18to the first pressure space 15.

In an alternative embodiment, the inner housing 3 and the outer housing2 can be configured with an overload inflow line 23 (not shown ingreater detail). External steam flows into the overload inflow line 23via a separate inflow.

In one preferred exemplary embodiment, the outward channel 14 isconnected to the flow channel 9 after a return blade stage 24 and thecrosswise return channel 20 is connected to the flow channel 9 after acrosswise return blade stage 25. Here, the crosswise return blade stage25 is arranged after the return blade stage 24 in the flow direction 11of the flow channel 9, with regard to expansion of the steam.

In one particularly preferred exemplary embodiment, the return bladestage 24 is the fourth blade stage and the crosswise return blade stage25 is the fifth blade stage.

A seal 27 is arranged between the inner housing 3 and the outer housing2 in the region of the thrust compensating piston 4. Said seal 27 isconfigured appropriately for example as a piston ring and is arranged ina groove 28 in the inner housing 3. As a result, the seal 27 separatesthe first pressure space 15 from a third pressure space 29. A pressurep₃ prevails in the third pressure space 29. The pressure p₃ can beapproximately equal to the pressure p₁. A further seal 30 delimits thethird pressure space 29. The further seal 30 is arranged between theinner housing 3 and the outer housing 2 and separates the third pressurespace 29 from the fourth pressure space 31, in which the pressure p₄prevails.

The third pressure space 29 is connected via a direct connection 32 tothe thrust compensating piston pre-space 12. The pressure p₂ prevails inthe thrust compensating piston pre-space, wherein p₂<p₃. The connection32 represents a flow connection and makes it possible that steam whichis situated in the third pressure space 29 can flow into the thrustcompensating piston pre-space 12. The steam present in the fourthpressure space 31 flows in the inner housing end region 33 onto a thrustcompensating piston surface 34 of the thrust compensating piston 4.

FIG. 2 shows a cross section through the steam turbine 1 in a sectionthrough an inflow 35. The inflow 35 comprises a valve diffuser 36. Freshsteam flows from the valve diffuser 36 into the inflow opening 10 andfrom there, as described with respect to FIG. 1, through the flowchannel 9. The steam which has flowed into the first pressure space 15can flow partially into an annular cooling channel 37 which is formedbetween the valve diffuser 36 and the outer housing 2. At a reversalpoint 38, the steam flows via a further cooling channel 39 in the outerhousing 2 to the third pressure space 29. From the third pressure space29, the steam flows via the connection 32 into the thrust compensatingpiston pre-space 12. Since the pressure p₁>p₃>p₄, a targeted forcibleflow is produced by this component region as a result whichadvantageously cools the valve connection 40. Effective cooling of thevalve connection 40 is therefore possible, without external coolingsteam being used. Here, the valve diffuser 36 is arranged sealingly onthe inner housing 3.

Contactless sealing elements, such as sealing bands, which realizepressure dissipation and separation of the pressure spaces are usuallyarranged between the rotor 5 and the inner housing 3 in the region ofthe thrust compensating piston 4, in particular in the leakage sealingspace 19 and a second leakage sealing space 41. In order to ensure thecooling of the valve connection 40, a return of the steam is necessaryfrom the thrust compensating piston pre-space 12 via the partial regionof the sealing space 18, further via the crosswise return channel 20 tothe inflow space 26 in the flow channel 9.

1. A steam turbine having an outer housing and an inner housing,comprising: a rotor, comprising a plurality of rotor blades, which has athrust compensating piston being arranged in a rotationally mountedmanner within the inner housing, the inner housing having an innerhousing end region which is formed around the thrust compensatingpiston, a seal which seals a third pressure space which is arrangedbetween the inner housing end region and the outer housing, the innerhousing having a feed channel which connects a first pressure space to athrust compensating piston pre-space which is arranged between thethrust compensating piston and the inner housing, the first pressurespace being arranged between the inner housing and the outer housing,wherein the steam turbine has a connection which connects the thirdpressure space in terms of flow to the thrust compensating pistonpre-space, a further seal being provided which is arranged between theinner housing and the outer housing, the third pressure space beingarranged between the seal and the further seal.
 2. The steam turbine asclaimed in claim 1, the seal being configured as a piston ring.
 3. Thesteam turbine as claimed in claim 1, the connection opening into thefeed channel.
 4. The steam turbine as claimed in claim 1, furthercomprising: a flow channel having a plurality of blade stages beingformed between the inner housing and the rotor, the inner housing havingan outward channel which is formed as a communicating line between theflow channel downstream of a blade stage and the first pressure space.5. The steam turbine as claimed in claim 1, further comprising: a valvefor feeding steam into the flow channel, and an annular cooling channelbeing formed in the valve, which wherein the annular cooling channel isconnected in terms of flow to the first pressure space.
 6. The steamturbine as claimed in claim 5, wherein the annular cooling channel isconnected in terms of flow to the third pressure space.
 7. The steamturbine as claimed in claim 5, wherein the valve comprising comprises avalve diffuser, and the annular cooling channel is arranged between thevalve diffuser and the outer housing.
 8. The steam turbine as claimed inclaim 5, comprising a further cooling channel being arranged in theouter housing as a space connection to the third pressure space.